Hitherto, an electronic watch including analog display means is generally configured to drive hands thereof with a step motor (also referred to as “stepping motor” or “pulse motor”). The step motor is formed of a stator to be magnetized by a coil and a rotor being a disc-shaped rotary body subjected to bipolar magnetization, and is generally involved in a fast-forward operation (high-speed driving) for moving the hands at high speed for time correction or the like as well as normal hand driving for moving the hands every second.
In the fast-forward operation, a driving pulse is supplied to the step motor at high speed with a short cycle period, but the step motor needs to operate without causing an error in the hand movement, that is, a rotation error of the rotor in response to the high-speed driving pulse with a short cycle period. Therefore, there has been proposed an electronic device including a step motor capable of stably conducting a fast-forward operation by detecting a rotation state of the rotor and supplying an appropriate driving pulse in accordance with the rotation state (refer to, for example, Patent Literature 1).
In Patent Literature 1, in the driving of the step motor, assuming that reverse induced power excited by rotation of the rotor is a current or a voltage, the first peak thereof is detected, and the driving pulse is supplied while presence or absence of the rotation of the rotor keeps being verified based on the detection, to thereby achieve the fast-forward operation. Further, in order to prevent an influence of spike noise ascribable to the driving pulse, there is disclosed setting an insensitive time period (mask time period) for inhibiting the reverse induced power from being detected for a predetermined time period from an output timing of the previous driving pulse, to thereby optimize a detection timing.
There has also been proposed a detection control device for a step motor, the detection control device being configured to detect a timing of damped oscillation at which a driving energy generated by a next driving pulse becomes positive from a reverse induced current generated by damped oscillation of a rotor, to thereby determine an output timing of the next driving pulse (refer to, for example, Patent Literature 2).
In Patent Literature 2, there is disclosed that, in order to detect the reverse induced current generated by the damped oscillation of the rotor and then obtain the timing at which the next driving energy becomes positive, the next driving pulse is output after a fixed delay time (d′mS). As a result, the energy of the damped oscillation of the rotor can be utilized effectively, and the current consumed by the driving can be reduced. In addition, the next driving pulse can be output without waiting for the damped oscillation of the rotor to decrease. Thus, the fast-forward operation can be conducted at higher speed than in the related art.